1. Field of the Invention
The present invention relates to a method and apparatus that provides differential connections with improved ESD protection and routing, and particularly a method and apparatus that provides differential connections which meet HDMI and DVI specifications.
2. Background of the Related Art
When routing high speed data signals between two points, it is well-known that many competing considerations exist in order to maintain the integrity of the signals.
For certain high speed lines, there is desired to maintain both integrity of the signal, as well as obtain electrostatic discharge (ESD) protection. These considerations can be at odds with each other, since providing ESD protection requires some type device that will add a capacitance or inductance to the line, thereby having an adverse effect on signal integrity.
In particular, HDMI has 4 pairs of differential, high speed data lines (TMDS lines) that must have tightly controlled impedance levels from an HDMI connector to the actual processing chip. Between the connector and this processing chip run impedance matched lines that are centered at 100 ohms and can differ by no more than +/−15% based on the HDMI specification. Adding any ESD device on top of these lines (i.e. capacitance and inductance) can cause discontinuities in the impedance producing a failure (according to the HDMI spec).
As a result, conventional interface devices that offer ESD protection for the HDMI and DVI specifications use multiple ESD protection chips or, as illustrated in FIGS. 1(a)-(c) route high speed lines in various circuitous paths, which then also lead to non-uniform parasitic return path impedance. As such, there is a significant increase in impedance discontinuities and increase induced parasitics when routed normally. Further, a greater area of board space is consumed. As a result, greater signal skew exists at the receiver because of uncontrolled parasitics from the different ESD devices.